Sensor check needed on aisle 4 please Mr. Fairdeal

[boscoe99]

Engine temperature sensor is connected to the ECU by a black and a black/yellow wire. Have you/can you measure the black/yellow wire for output voltage please? Someone on TOS thinks it should be five volts. If so, I am wondering why the orange wire is not used.

[fairdeal]

I will check that tomorrow;
boat is in the water but shouldn't be too exciting to access that sensor connector -
think its right on top - just have to remove the flywheel cover.

I will also check the air temp sensor, which is also a two-wire sensor
(I'm thinking all the rest are 3-wire)

I won't be surprised if its ~5V
that is fairly typical for simple resistance sensors: fuel level sender, trim sender
and I assume its tightly regulated for a reliable reading -
as opposed to using "12V system voltage" -
which is going to constantly vary by several volts

the "orange wire" is not used for the two-wire sensors
because, just like a fuel gauge,
the "gauge" (in this case the ECM)
has to "measure how much electricity is flowing to ground"
through the variable resistance of the sensor.

If there were other devices sharing that con*****ed power source,
as their resistance varied, it would throw off the reading

[fairdeal]

engine temp sensor, black/yellow to ground:




air temp sensor, black/yellow to ground:

[99yam40]

I wonder why the voltage is a little lower on the air temp.

do you think the ECU has a different voltage regulating source for each sensor.
I think it should have one that feeds them all.
if something drags it down all sensors are off

[boscoe99]

Thanks Fairdeal. Good intelligence.

I am now wondering why Yamaha does not use an orange wire for the resistor senders.

And why it is not the same orange as the other orange wires. I read what you say but right now it is not computing in my brain. If the 5 volt power supply has the ability to provide X current while maintaining 5 plus or minus Y volts it should not matter. Current flow is nil in almost all cases. I think.

And why the orange wire is not monitored for at least output voltage at the ECU.

Oh well. It will remain a mystery.

[fairdeal]

I could be mistaken - but here's my take

with a "two wire sensor" - the gauge (or for the sensors under discussion, the ECM)
is acting as an "ammeter" in a simple application of Ohms law: I = V/R

with the voltage held steady,
the varying resistance of the sensor, results in a varying current passing to ground.
The gauge "measures the current" and converts to a temperature / fuel level / trim level / whatever.

So anything else in that circuit - any parallel path to ground - or resistance in series -
would throw off the "conversion" of current flow to data.

Conversely, with 3-wire senders, the "reference voltage" also needs to be held constant -
but otherwise, nobody care how many amps of it are flowing to ground -
the gauge/ECM only cares what voltage is "split off" by the sensor and returned on the 3rd wire.

[99yam40]

In that thinking, do you think the ECU has separate voltage regulation for each 2 wire sensor?
or just one that feeds all of the 2 wire sensors and another one for the 3 wire?

I would think that a common power source could work, just monitor the return wire current, or do all of the black wires run back to a common ground?

[fairdeal]

The early F225 - through my 2005 model, use a separate ECM pin for each 2-wire sensor (power)
and all grounds are common.

Interestingly,
while my 2005 used a single common power source for all 3-wire sensors-
including two "newly added" Command Link sensors

the earlier models used a separate ECM pin for power to each 3-wire sensor



whether they were actually "sourced separately" inside the ECM, I can't say
(btw there is an error in the diagram, above -
the ground connection for the oil pressure sensor is not shown)

[boscoe99]

I suspect that only Mitsubishi really knows what is going on.

Ganged orange wire leads, separate non-ganged orange wire leads but no ganged black/yellow wire leads.

Ganged black wire leads and separate non-ganged ground leads.

[ausnoelm]

It's pretty common in electronics to have a common 5V "rail" but also have individual 5V supplies too, and there is various reasons for it, in this instance (and I am only guessing here, unless someone can supply a full circuit diagram of the ECU) if a sensor goes out of range, it can do a couple of things, reduce engine speed, set an alarm and so on, which sensor does this is not important, because the required result is the same, but, if you need a certain sensor to do something else, like maybe move a gauge reading, it may require its own 5V reference, or if this sensor needs to "know" certain parameters for starting, it might require a seperate reference source to other devices, it's stupidly simple, in operation, yet very complicated at the same time when how it happens is taken into account, to most, how it happens doesn't matter, because a black box does it all for you, but, someone had to manufacture that black box.

[99yam40]

many voltage regulated low voltage supplies seems a strange way to do this, but maybe they used just one or two.
who knows how they worked all of this

[zenoahphobic]

5 volt regulators are everywhere and cheap. Probably because they are relatively low current devices. There is a sharp cost increase in making a regulator high current; that often sees a number of small current voltage regulators still cheaper than using one bigger one.
Also from a technical requirement point of view, the higher the current requirements the more difficult it is to keep the voltage steady.
Many chips have complex circuits within them, and creating a number of 5 volt regulators within them is easily accommodated. We see less and less of what the circuits are within chips, and care lesser these days.

[boscoe99]

Found this on the innerweb. I am guessing that it depicts the situation within a Yamaha ECU.

The Yamaha SM only makes mention of testing the sensor itself. However, if the voltage output was low to begin with, or the wires had excessive resistance, or a wire was broken, then the voltage sensing component would receive an incorrect voltage. Which would fool the ECU.

Does it seem strange that no testing for the circuit itself is provided? Is this just Yamaha?

[fairdeal]

Nice diagram -
has me wondering why they made a point of showing a fixed in-line resistor with the sensor

is that connected in parallel with the thermally-variable resistor?
so theres alway a fixed minimum resistance - even if the sensor is "open"?

[boscoe99]

I see the fixed resistor as being in series with the variable resistor. I could see it as being a voltage trim device so as to affect the input voltage that is seen by the voltage sensing circuit.

I did not pick up on the apparent parallel connection at the wiring interface to the variable resistor. I suspect this is a drawing error. But ???

Damnit. Back to the drawing board.